March 10, 2003

UCSC astronomer John Faulkner to address U.K. astronomy meeting

By Tim Stephens

The Royal Astronomical Society (RAS) has invited John Faulkner, professor of astronomy and astrophysics, to give the Roger Tayler Memorial Lecture at the National Astronomy Meeting next month in Dublin.

Faulkner's talk, which will take place on April 10, will be the last in a series of five annual lectures established by the RAS to honor Tayler after his death in 1997.

Tayler was a highly distinguished physicist and astronomer who did pioneering work in several areas of research. He served the RAS for many years, first as secretary, then as treasurer, and finally as president. He was also the managing editor of the society's major journal for 20 years.

Faulkner worked with Tayler at Cambridge University when Faulkner was a graduate student of Fred Hoyle, another giant in the field of astronomy. At the time, Hoyle had so many graduate students working with him that he decided he needed another senior researcher to help guide them, Faulkner said.

"[Hoyle] brought Tayler back to Cambridge to help mentor this large group of graduate students, and he was very good at that," Faulkner said. "He was really a delightful guy and he did some very important work in those early days. Later he became a much loved president of the Royal Astronomical Society. So I really felt honored to receive the invitation to give the final lecture in this series."

The National Astronomy Meeting at which Faulkner will give the lecture brings together all of the major astronomy organizations of the United Kingdom and the Irish Republic. The title of Faulkner's lecture is "Standing on the Shoulders of Dwarfs," a sly twist on one of Isaac Newton's most famous remarks that Faulkner has used to describe his work on the structure and evolution of stars.

Stellar evolution is an area in which both Tayler and Faulkner made significant contributions, and it continues to be the primary focus of Faulkner's research. In 1966, Faulkner published a landmark paper explaining a key phase in the life of stars like the Sun, which are known to astronomers as red dwarfs. His most recent work not only explains another key phase of stellar evolution (the "red giant" phase), but also provides a unifying viewpoint that links all three major stages in the evolution of stars like the Sun.

The Sun is currently in the first of these major stages, the "main sequence" phase, which accounts for about 90 percent of the life of a star. When a main sequence star starts to exhaust the hydrogen fuel in its core, the core begins to condense while the outer portions of the star expand. It then becomes an extremely large "red giant," with a very dense core and a large outer envelope.

Eventually, the core becomes hot enough to burn helium and the star enters the "horizontal branch" phase, the third major stage in its evolution. Finally, most of the outer portions of the star are blown off and it becomes a "white dwarf."

Faulkner's 1966 paper explored computationally the strange structure of stars in the horizontal branch phase, with their double energy source of helium and hydrogen. His new work explains analytically why stars become red giants, and also sheds new light on the other two main stages in the evolution of stars like the Sun.

"Not only does the red giant build on the previous red dwarf stage, but what is developing in the interior of the red giant is like a white dwarf, the obvious precursor of the bare white dwarf it will ultimately become," Faulkner said.

The Sun is about half way through the main sequence phase of its evolution. It will remain essentially unchanged for another 5 billion years or so before it swells up to become a red giant 150 to 200 times its current size.

"A red giant is like a white dwarf with a storage problem. And, as many of us might consider doing when faced with this problem, it remodels the attic. That's why and how it gets that big," Faulkner said.

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